1. Field of the Invention
The present invention relates to a semiconductor laser and a method of manufacturing the same, and more particularly to a semiconductor laser and a method of manufacturing the same wherein solder layers used for stacking a plurality of semiconductor laser chips cause no interference with laser beam radiation.
2. Description of the Prior Art
Conventionally, a semiconductor laser has been composed of a semiconductor laser chip stack having semiconductor laser chips laminated one above another by soldering. Such a prior art semiconductor laser is disclosed, for example, in Japanese Laid-Open Patent Publication Nos. 4-48664 and 478179. Such a semiconductor laser chip stack is suitable for providing high output.
FIG. 7 shows a sectional structure of such a prior art semiconductor laser. In FIG. 7, a semiconductor laser chip stack 70 is composed of semiconductor laser chips 71, 72 and 73 laminated one above another and joined to one another by respective solder layers 74 and 75.
The semiconductor laser chip 71 includes an active layer 71a which is formed at an end thereof with a laser beam radiating surface 71b. Similarly, the semiconductor laser chip 72 includes an active layer 72a which is formed at an end thereof with a laser beam radiating surface 72b, and the semiconductor laser chip 73 includes an active layer 73a which is formed at an end thereof with a laser beam radiating surface 73b.
The laser beam radiating surfaces 71b, 72b and 73b are arranged in a common plane. A laser beam 71c is emitted from the laser beam radiating surface 71b, a laser beam 72c from the laser beam radiating surface 72b, and a laser beam 73c from the laser beam radiating surface 73b.
In the above prior art, however, due to load applied when the semiconductor laser chip stack 70 is formed in layers, a solder flash 74a is formed at the end of the solder layer 74 and a solder flash 75a at the end of the solder layer 75. If formation of such flashes is to be avoided, the connecting strength will become disadvantageously insufficient, resulting in separation of chips and increase of connecting resistance.
Thus, the solder flash 74a interferes with the laser beam 71c, and the solder flash 75a interferes with the laser beam 72c, so that the laser beams 71c and 72c are restricted as shown in FIG. 7. Consequently, the prior art involves a defect that luminous efficiency of radiation of the semiconductor laser chip stack 70 is substantially reduced.